PROJECT SUMMARY/ABSTRACT Although the unfolded protein response (UPR) as a consequence of endoplasmic reticulum (ER) stress emanat- ing from an intestinal epithelial cell (IEC) is well recognized to promote inflammation, little is known about the ways that an IEC-derived UPR regulates other non-canonical functions. Recently, we discovered that an IEC- associated UPR can regulate transmission of factors into the tissues or intestinal lumen that affect immune responses or the composition of the microbiota, respectively. The current research proposal addresses the un- answered question of how the UPR mediated regulation of factors involved in immune and microbiota function are important to inflammatory bowel disease (IBD), metabolic syndrome and susceptibility to enteropathogens. Our long-term goals are to parse out the specific mechanisms and consequences of UPR-mediated regulation of factors involved in immune and microbiota function important to these (patho)physiologic activities. The ob- jective of this research is to specifically define how an IEC-associated UPR can cause the sterile induction of Thelper17 (TH17) cells in tissues or regulate the luminal microbiome through affecting intelectin-1 (ITLN1) pro- duction, an elusive microbial lectin of poorly understood activity, that is increased in IBD and decreased in obe- sity. Our central hypothesis is that IEC-associated ER stress regulates the release of factors which affect a variety of physiologic functions important to immune development and regulation of the microbiome. The ra- tionale for our proposed research is that developing such insights into these mechanisms will shed important light on how they might lead to new perspectives on elucidating the role played by IEC-associated ER stress in regulating TH17 cell development through control of interleukin-6 and IEC-derived ITLN1 function as a risk factor for IBD and metabolic syndrome through the control of specific microbes. Our central hypothesis will be tested with three specific aims: 1) define the involvement of IEC ER stress in the sterile induction of TH17 cells; 2) identify how IEC-associated ER stress affects ITLN1 regulation of the microbiome, and; 3) characterize the con- sequences of ITLN1-deficiency on immunometabolic function. In Aim 1 we will use a newly developed model of ER stress induction through selective expression of a glucose-regulated protein 78 (GRP78) inhibitor in the ER and other models to reveal how a UPR in the IEC instructs intestinal TH17 cell development independently of microbiota and the role played in microbial TH17 induction. Aim 2 will define ITLN1 as a UPR-regulated, IEC- derived lectin which binds a limited range of pathobionts using a newly developed technique of ITLN1-Seq and how this regulates the induction of colitis. Aim 3 will provide direct evidence that ITLN1 regulation of specific microbiota will act as a causal factor in obesity. Overall, this proposal is significant because it will allow us to understand how IEC-associated ER stress broadcasts itself into the tissues or lumen to regulate the host and/or the microbiota, respectively, and provide new dimensions on our understanding of several non-canonical activi- ties of an IEC-associated UPR.